1. Field of the Invention
This invention relates to monitors for the contents of containers and more particularly to such monitors which detect when the contents of a container are below some predetermined level. The invention has particular applicability to monitoring the level of fluid in reservoirs used to progressively administer solutions to hospital patients.
2. Background Art
Parenteral and enteral solutions are routinely administered to hospital patients through sterile administration sets, which are frequently disposable. Normally, the administration set is removed from its sterile package and connected to a sterile reservoir of the fluid through a spike or cannula that is part of the administration set. The administration set is then filled for priming purposes with the fluid, and a second cannula is used to effect actual connection between the primed administration set and the patient.
As the administration of fluid proceeds, the sterile reservoir becomes progressively depleted. If the reservoir is allowed to go completely empty, continued flow of the fluid will either partially or completely deplete the fluid remaining in the administration set itself.
The presence of any air in the tubing below the drip chamber can not only be a major inconvenience, it can also be a potential hazard to the patient. Once air gets into the tubing leading from a drip chamber to a patient, it effectively precludes continued use of the administration set for the delivery of fluids. Indeed, if this air is not purged from the tubing of the administration set prior to an attempt to administer additional fluid, any fluid subsequently added to the drip chamber or the fluid reservoir thereabove will force an air bolus into the patient. As a practical matter, air in the tubing set can only be removed by either injecting a saline solution into the administration set below the fluid level, or by disconnecting the administration set from the patient and repeating the priming procedures. Either option disrupts the administration of fluids to the patient and increases the risk of inducing bacterial infection.
Various types of mechanical floats, electronic drop detectors, and ultrasonic level detectors exist for the purpose of monitoring the contents of a container, such as the drip chamber in an administration set. As presently implemented, however, each has significant drawbacks.
Mechanical floats are generally disposed to operate a valve located internally to the administration set. The valve is generally in its open position in the presence of a fluid and in its closed position in the absence thereof. Common forms of mechanical floats include a floating disk or a floating ball that occludes an exit port when the level of fluid in the chamber in which the valve has been installed drops sufficiently. Nevertheless, when used as components of a disposable administration set, such devices add significantly to the cost involved.
Accordingly, several monitors have been developed that operate externally to an administration set and that can therefore be reused, saving substantial costs. Among these are electronic devices which can be generally subclassified as optical detectors or ultrasonic detectors.
Several examples can be given of optical devices that operate in conjunction with a drip chamber in an administration set. Typically, such detectors are positioned externally to the administration set to achieve an interruption or deflection of a fixed light beam by drops of fluid falling through a space between one or more light sources and light detectors. The absence at expected intervals of signals responsive to such falling drops is used to indicate the depletion of the fluid in a sterile reservoir.
Optical drop detectors require complex devices to define what time interval between drops constitutes an accepted interval. Further, the optical devices are frequently sensitive to ambient light levels and will often generate erroneous signals due to momentary changes in these levels. In addition, these types of detectors are susceptible to misreadings due to fog forming on the interior wall of the drip chamber which can either obscure the beam of light or trigger false signals through drops of condensed fluid vapor meandering down the drip chamber wall.
In a slightly different operation from the optical detector, ultrasonic fluid level detectors generally utilize the fluid present in the lower half of the drip chamber as a conduit for an ultrasonic signal from a sending transducer. The failure of a receiving transducer to detect the ultrasonic signal which is normally transmitted when fluid fills the lower half of the drip chamber is taken as an indication that fluid has been depleted in the region of the drip chamber which was previously used as a conduit for the ultrasonic beam. Proper coupling of the ultrasonic unit to the administration set requires that both the sending and receiving transducers of the ultrasonic unit be in intimate contact with the walls of the drip chamber. Unfortunately, any significant variation in drip chamber dimensions of different administration sets can obviate this required intimate contact. In addition, the high cost of generating, coupling, receiving, and detecting ultrasonic beams can be major drawbacks in the cost effectiveness of ultrasonic devices.
In light of the above, an object of the present invention is to provide an improved monitor for the contents of a container which will detect when the contents are below a predetermined level.
Another object of the present invention is to provide a monitor as described above which is used externally to the container being monitored, so that the monitor may be reused with successive disposable containers.
Still another object of the present invention is a monitor for the contents of a container which does not depend for its successful operation on measuring the rate of dripping of the fluid from that container. Thus, both generally and in the specific instance mentioned, it is an object of the present invention to eliminate the need to determine and adjust the monitor to any predetermined rate of material or fluid flow in order to monitor the level thereof.
An additional object of the present invention is to produce a monitor as described above that does not require an intimate fit with the exterior of the container in which contents are to be monitored and thus is operable with containers having differing dimensions.
Yet another object of the present invention is to provide a monitor as described above which is not susceptible to erroneous functioning due to light ambient conditions.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.